Composite wood replacement article and method of making same

ABSTRACT

A composite article includes a matrix having first and second opposing surfaces defining a transverse dimension and a filler material embedded in the matrix. The filler material presents a density gradient in the transverse dimension wherein a minimum filler density is at the first surface. In one embodiment, the composite article is a non-laminated article defining first and second regions wherein the first region encompasses the first surface. The first region has a filler-to-matrix ratio that varies along the transverse dimension, the filler-to-matrix ratio being at a minimum at the first surface. The first region can include one or more additives. A method for forming a composite article includes injecting first and second compositions into a die head at different points so as to produce a partially mixed composition that is discharged from the die head. The second composition contains less filler material than the first composition.

BACKGROUND OF THE INVENTION

This invention relates generally to wood replacement materials (i.e.,materials suitable for use as a replacement for natural wood) and moreparticularly to composite wood replacement articles and extrusionprocesses for forming such articles.

Although wood is a naturally reproducible resource, the supply of goodwood for construction and other purposes is diminishing because of alarge worldwide demand for wood products. Accordingly, there isincreasing interest in developing wood replacement products. Woodcomposites represent one such replacement product. Wood compositescomprising a combination of recycled wood scraps (such as wood meal,wood chips, sawdust, newspapers and the like, which are by-products ofindustrial processes and other industries using natural wood products)and a thermoplastic material have been known for many years. Generally,these composites are formed so that they may be used in many of the sameapplications as natural wood products, while offering advantages such ashigh resistance to rot, insects, and moisture. These products can havethe same workability as wood and are typically splinter-free.

It is common with wood composites to include various additives toprotect against discoloration, mildew, ultraviolet light exposure, etc.However, such additives can be very expensive, particularly when theadditives are incorporated throughout the entire wood compositecomponent. To address the high cost of these additives, multi-layer orlaminated wood composite products comprising a substrate layer and athin cap layer disposed on at least one surface of the substrate layerhave been proposed. The substrate layer comprises a polymer/fibermixture that produces the primary advantages of wood composites, i.e.,wood-like stiffness and strength and low contraction and expansion. Thecap layer comprises a mixture of polymer and additives, such as pigmentsand stabilizers, for protecting the substrate layer. By limiting theadditives to the thin cap layer, this approach reduces the amount andcost of the additives while still providing the desired protection. Adrawback of these laminated wood composites, however, is that thedistinct cap layer can be susceptible to delamination and/or a negativemarket perception.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a composite articleincluding a matrix having first and second opposing surfaces defining atransverse dimension and a filler material embedded in the matrix. Thefiller material presents a density gradient in the transverse dimensionwherein a minimum filler density is at the first surface.

In another embodiment, the present invention provides a non-laminatedcomposite article having first and second opposing surfaces defining atransverse dimension. The non-laminated composite article includes amatrix and a filler material embedded in the matrix and defines firstand second regions juxtaposed along the transverse dimension wherein thefirst region encompasses the first surface. The first region has afiller-to-matrix ratio that varies along the transverse dimension, thefiller-to-matrix ratio being at a minimum at the first surface. Thefirst region can include one or more additives.

In yet another embodiment, the present invention provides a method offorming a composite article having first and second opposing surfacesdefining a transverse dimension. The method includes providing a diehead having an outlet and injecting a first composition into the diehead at a first point to create a first stream. The first compositionincludes a combination of matrix and filler materials. The methodfurther includes injecting a second composition into the die head at asecond point to create a second stream. The second composition containsless (or no) filler material than the first composition. The secondpoint is located relative to the outlet so as to permit a degree ofmixing between the first and second streams so as to produce a partiallymixed composition stream that is discharged through the outlet.

The present invention and its advantages over the prior art will be morereadily understood upon reading the following detailed description andthe appended claims with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the concluding part of thespecification. The invention, however, may be best understood byreference to the following description taken in conjunction with theaccompanying drawing figures in which:

FIG. 1 is a perspective view of a composite article in accordance with afirst embodiment of the present invention.

FIG. 2 is a side view of the composite article of FIG. 1.

FIG. 3 is a graph plotting the filler-to-matrix ratio against articlethickness for the composite article of FIG. 1.

FIG. 4 is a schematic view of an extrusion system capable of forming acomposite article.

FIG. 5 is a side view of a composite article in accordance with a secondembodiment of the present invention.

FIG. 6 is a graph plotting the filler-to-matrix ratio against articlethickness for the composite article of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIGS. 1 and 2 show acomposite article 10 that can function as a wood replacement product. Inthe illustrated embodiment, the composite article 10 is a board havingsix planar surfaces: first and second opposing faces 11 and 12, firstand second opposing sides 13 and 14, and first and second opposing ends15 and 16. The composite article 10 defines a first transverse dimensiona, also referred to as the thickness, a second transverse dimension b,also referred to as the width, and a longitudinal dimension c, alsoreferred to as the length. The dimensions a, b and c can be of anydesired value. For instance, the composite article 10 could be a 1″×6″board that is 8 feet long or a 2″×4″ board that is 10 feet long. Itshould be noted that the flat board configuration shown in FIGS. 1 and 2is shown only by way of example. The present invention is not limited tothis particular configuration and will apply to composite articleshaving many other shapes and sizes.

The composite article 10 generally comprises a matrix having a fillerembedded therein. Any desired combination of matrix and filler materialscan be used, although for wood replacement products the matrix willtypically comprise a plastic material and the filler will typicallycomprise a cellulosic material. Examples of suitable matrix materialsinclude, but are not limited to, polymers such as polypropylene, highdensity polyethylene (HDPE), low density polyethylene (LDPE), polyvinylchloride (PVC), chlorinated polyvinyl chloride (CPVC), acrylonitrilebutadiene styrene (ABS), ethyl-vinyl acetate (EVA), and polystyrene.Preferred cellulosic filler materials include, but are not limited to,sawdust, newspaper, alfalfa, wheat pulp, wood scraps (e.g., ground wood,wood flour, wood flakes, wood chips, wood fibers, wood particles), woodveneers, wood laminates, cardboard, straw, cotton, rice hulls, paper,coconut shells, peanut shells, bagasse, plant fibers, bamboo fiber, palmfiber, kenaf, and mixtures thereof. In one embodiment, the averageparticle size of the cellulosic filler material is less than about ½inch, and preferably from about 1/32- 1/16 inch. In addition, theparticles of the cellulosic filler material have an average aspect ratio(i.e., the ratio of the length to the widest thickness) of at leastabout 10:1, preferably at least about 20:1, and more preferably fromabout 30:1 to about 50:1. The use of such long particles increases theflexural modulus of the composite article, thus providing a stiffnesscomparable to natural wood.

The composite article 10 can also include a number of optionaladditives, such as process aids, lubricants, stabilizers, accelerators,inhibitors, enhancers, and colorants, which modify or adjust certainproperties of the composite article. As will be described in more detailbelow, the use of such additives is generally limited to one or morespecific regions of the composite article 10. Examples of such additivesinclude, but are not limited to, UV stabilizers (e.g., CYTEC 38535,CYTEC 3346) and acrylic process aids (e.g., Rohm and Haas K175, KanekaKane-Ace PA-101). Examples of lubricants include zinc stearate, calciumstearate, esters, amide wax, paraffin wax, ethylene bis-stearamide, andother suitable materials.

The composite article 10 is a non-laminated article. That is, thecomposite article 10 does not comprise distinct layers, but only asingle layer. The composite article 10 defines two regions 18 and 20 ofdiffering compositional makeups. In the illustrated embodiment, the tworegions 18 and 20 are juxtaposed along the first transverse dimension(i.e., across the thickness) so that first region 18 encompasses thefirst face 11 and the second region 20 encompasses the second face 12.Generally, the second region 20 comprises a large majority of thethickness of the composite article 10 and is thus thicker than the firstregion 18. In one embodiment, the first region 18 is approximately 1/16to ⅛ inches deep, with the second region 20 comprising the remainder ofthe article thickness.

The two regions 18 and 20 both generally comprise a matrix-fillercomposite but have differing compositional makeups. Namely, the firstregion 18 has a lower filler content than the second region 20. Althoughthe first region 18 contains less filler than the second region 20, itis generally preferred that the filler content of the first region 18 isnot zero. The first region 18 preferably contains some filler in orderto enhance the wood-like appearance of the first face 11. In oneembodiment, the first region 18 comprises approximately 1-2% filler byweight and the second region 20 comprises approximately 60% filler byweight.

In addition, the first region 18 preferably includes one or moreadditives, such as the additives described above, which are not includedin the second region 20. In other words, only the first region 18 hasthe additives, thereby achieving the benefits of the additives at thefirst face 11, but reducing the cost by not having additives throughoutthe entire thickness of the board. The thick second region 20, with itshigh filler content, lends wood-like stiffness and strength to thecomposite article 10. It is possible that the second region 20 includessome additives or materials other than matrix and filler, but therelatively high concentrations of protective additives of the typediscussed above are generally limited to the first region 18.

The filler material in the first region 18 is distributed so as topresent a density gradient along the first transverse dimension of thecomposite article 10, with the minimum filler density being at the firstface 11. That is, the filler content varies in density or concentrationacross the thickness of the first region 18. Another way of stating thisis that the ratio of filler material to matrix material (the“filler-to-matrix ratio”) varies in the transverse dimension in thefirst region 18, and specifically decreases approaching the first face11. This is depicted graphically in FIG. 3, which plots thefiller-to-matrix ratio across the thickness of the composite article 10.As shown, the filler-to-matrix ratio is at a uniform maximum in thesecond region 20 and decreases in the first region 18, with the minimumratio (and hence minimum filler density) occurring at the first face 11.While the rate of change of the filler-to-matrix ratio in the firstregion 18 is shown to be linear in FIG. 3, it should be noted that thisrate of change could also be non-linear.

While the above description describes the filler density gradient asoccurring along the first transverse dimension, it should be noted thatan alternative embodiment is possible in which the filler densitygradient occurs along the second transverse dimension b (i.e., acrossthe width of the composite article 10). In this case, one of the sides13 and 14 would present an additive-protected surface having a minimumfiller density. It is also possible to provide a filler density gradientalong the longitudinal dimension c, or length, of the composite article10, although there may not be much benefit in making one of the ends 15and 16 an additive-protected surface.

Referring now to FIG. 4, one method of forming the composite article 10is shown. In this approach, the composite article 10 is extruded usingan extrusion system 22 having first and second extruders 24 and 26connected to a die head 28. The first extruder 24 injects a firstcomposition into the die head 28 at a first point 27, and the secondextruder 26 injects a second composition into the die head 28 at asecond point 29. The die head 28 has an outlet 31 through which extrudedmaterial is discharged.

The first extruder 24 comprises a barrel 30 having an internal chamber.A screw 32 is rotatively mounted in the chamber of the barrel 30.(Although single screw extruders are shown in FIG. 4, it should be notedthat the multi-screw extruders having two or more intermeshing screwscould alternatively be used.) The screw 32 is provided with one or morehelical threads such that, when rotating, the screw 32 will convey rawmaterials through the barrel chamber. The mechanical action of the screw32 will also heat and mix the raw materials. In addition, barrelheaters, such as electrical resistance heaters or the like (not shown),can be provided for providing additional heating of the raw materials inthe barrel chamber. The raw materials or ingredients making up the firstcomposition are physically mixed or blended (typically in powder orpellet form) in a feeder 34 such as a weigh blender. These mixedingredients are delivered from the feeder 34 to the first extruder 24through an inlet 36 formed in the barrel 30, typically near the firstend thereof. Preferably, the feeder 34 is positioned immediately abovethe extruder inlet 36, so that the blend of ingredients is formedimmediately prior to entering the first extruder 24, thus minimizing orpreventing separation of the ingredients. In the first extruder 24, theingredients are processed at a suitable speed and temperature and thenforced into the die head 28 at the first injection point 27.

In one embodiment using polyethylene and wood fiber ingredients, thescrew 32 is rotated at a rate of about 10-50 rpm, and preferably about15-34 rpm, to advance the ingredients through the extruder barrel 30 andinto the die head 28. Preferably, the screw 32 has a compression ratioof from about 2:1 to about 4:1, and more preferably from about 2.8:1 toabout 3.6:1. The temperature of the ingredients in the extruder barrel30 is preferably about 150-260° C., and more preferably about 175-230°C. The retention time of the ingredients in the barrel 30 is about20-120 seconds, and more preferably about 40-80 seconds. Finally, theingredients are advanced through the barrel 30 at a rate of about500-2,000 lbs/hr., and more preferably about 1,000-1,500 lbs/hr.

The second extruder 26 comprises a barrel 38 having an internal chamberand a screw 40 rotatively mounted in the chamber of the barrel 38. Theraw materials or ingredients making up the second composition arephysically mixed or blended (typically in powder or pellet form) in afeeder 42 such as a weigh blender. These mixed ingredients are deliveredfrom the feeder 42 to the second extruder 26 through an inlet 44 formedin the barrel 38, typically near the first end thereof. In the secondextruder 26, the ingredients are processed at a suitable speed andtemperature and then forced into the die head 28 at the second injectionpoint 29, which is located downstream from the first injection point 27.

In one possible embodiment, the first composition comprises acombination of a matrix and a filler. As mentioned previously, possiblematrix materials include, but are not limited to, polymers such aspolypropylene, high density polyethylene (HDPE), low densitypolyethylene (LDPE), polyvinyl chloride (PVC), chlorinated polyvinylchloride (CPVC), acrylonitrile butadiene styrene (ABS), ethyl-vinylacetate (EVA), and polystyrene. Possible filler materials include, butare not limited to, sawdust, newspaper, alfalfa, wheat pulp, wood scraps(e.g., ground wood, wood flour, wood flakes, wood chips, wood fibers,wood particles), wood veneers, wood laminates, cardboard, straw, cotton,rice hulls, paper, coconut shells, peanut shells, bagasse, plant fibers,bamboo fiber, palm fiber, kenaf, and mixtures thereof. The secondcomposition includes a matrix material (typically, but not necessarily,the same matrix material as in the first composition) preferablycombined with one or more additives such as process aids, lubricants,stabilizers, accelerators, inhibitors, enhancers, and colorants. Thesecond composition also contains less filler material than the firstcomposition. Here, “contains less filler material” can mean that eitherthe second composition includes some filler material but a smalleramount than the first composition or the second composition contains nofiller at all.

The first composition is injected into the die head 28 through the firstinjection point 27 so as to create a first stream 46 in the die head 28.The second composition is injected into the die head 28 through thesecond injection point 29 so as to create a second stream 48 in the diehead 28, which flows into the first stream 46. The second injectionpoint 29 is positioned on the die head 28 such that the second stream 48is located at what will become the first face 11 of the compositearticle 10. The second injection point 29 is located relative to the diehead outlet 31 so as to permit some mixing between the first compositionstream 46 and the second composition stream 48 to produce a partiallymixed composition stream that is discharged through the outlet 31.Specifically, the second injection point 29 is located a distance, L,upstream from the outlet 31 that is sufficient to allow a desired degreeof mixing between the two streams 46 and 48 before being dischargedthrough the outlet 31. The partially mixed composition is forced out ofthe die head 28 through the outlet 31 and assumes the desired shape ofthe composite article 10. The two streams 46 and 48 do not completelymix, but the incomplete mixing of the streams 46 and 48 results in anextruded composite article 10 having the first and second regions 18 and20 of differing compositional makeup. The first region 18 comprises amix of the first and second compositions, and the second region 20comprises only the first composition.

The extruded composite article 10 discharged from the die head 28 is cutto the desired length by a conventional cutter. Prior to being cut, theextruded composite article 10 can be cooled in a cooling chamber (notshown) and embossed with a suitable embossing device (not shown) toimpart a desired surface design such as one that simulates wood grain.

Referring to FIGS. 5 and 6 a second embodiment of a non-laminatedcomposite article 110 is shown. The composite article 110 defines threeregions 118, 119 and 120 of differing compositional makeups that arejuxtaposed along the first transverse dimension (i.e., across thethickness). In this case, the first region 118 encompasses the firstface 111 of the composite article 110, and the third region 120encompasses the second face 112. The second region 119 is positionedbetween the first and third regions 118 and 120. Generally, the secondregion 119 comprises a large majority of the thickness of the compositearticle 110 and is thus thicker than the first and third regions 118 and120, which are typically of equal thickness.

The three regions 118, 119 and 120 all generally comprise amatrix-filler composite, but have differing compositional makeups.Namely, the first and third regions 118 and 120 have a lower fillercontent than the second region 119. Although the first and third regions118 and 120 contain less filler than the second region 119, it isgenerally preferred that the filler content of the first and thirdregions 118 and 120 is not zero. The first and third regions 118 and 120preferably contain some filler in order to enhance the wood-likeappearance of the first and second faces 111 and 112. In one embodiment,the first and third regions 118 and 120 each comprise approximately 1-2%filler by weight and the second region 119 comprises approximately 60%filler by weight.

In addition, the first and third regions 118 and 120 preferably includeone or more additives, such as the additives described above, which arenot included in the second region 119. In other words, only the firstand third regions 118 and 120 have the additives, such asantimicrobials, thereby achieving the benefits of the additives at thefirst and second faces 111 and 112, but reducing the cost by not havingadditives throughout the entire thickness of the board. The cost savingsrealized with this second embodiment may not be as significant as thoseseen with the first embodiment, but both of the first and second faces111 and 112 receive the benefits added by the additives. The thicksecond region 119, with its high filler content, lends wood-likestiffness and strength to the composite article 110. It is possible thatthe second region 119 includes some additives or materials other thanmatrix and filler, but the relatively high concentrations of protectiveadditives of the type discussed above are generally limited to the firstand third regions 118 and 120.

The filler material in the first and third regions 118 and 120 isdistributed so as to present a density gradient along the firsttransverse dimension of the composite article 110, with minimum fillerdensity being at the first and second faces 111 and 112. That is, thefiller content varies in density or concentration across the thicknessof the each of the first and third regions 118 and 120. Another way ofstating this is that the filler-to-matrix ratio varies in the transversedimension in the first and third regions 118 and 120, and specificallydecreases approaching the first and second faces 111 and 112. This isdepicted graphically in FIG. 6, which plots the filler-to-matrix ratioacross the thickness of the composite article 110. As shown, thefiller-to-matrix ratio is at a uniform maximum in the second region 119and decreases in the first and third regions 118 and 120, with theminimum ratio (and hence minimum filler density) occurring at the firstface 111. While the rate of change of the filler-to-matrix ratio infirst and third regions 118 and 120 is shown to be linear in FIG. 6, itshould be noted that these rates of change could also be non-linear.

While specific embodiments of the present invention have been described,it will be apparent to those skilled in the art that variousmodifications thereto can be made without departing from the spirit andscope of the invention as defined in the appended claims.

1. A composite article comprising: a matrix having first and secondopposing surfaces defining a transverse dimension; and a filler materialembedded in said matrix, said filler material presenting a densitygradient in said transverse dimension wherein a minimum filler densityis at said first surface.
 2. The composite article of claim 1 whereinsaid transverse dimension is the thickness of said composite article. 3.The composite article of claim 1 wherein said composite article definesfirst and second regions juxtaposed along said transverse dimension,said first region encompassing said first surface and having a lowerfiller content than said second region.
 4. The composite article ofclaim 3 wherein said second region is substantially larger than saidfirst region and encompasses said second surface.
 5. The compositearticle of claim 3 wherein said filler density gradient is located insaid first region.
 6. The composite article of claim 3 wherein saidfirst region includes an additive.
 7. The composite article of claim 3wherein said composite article further defines a third region juxtaposedwith said second region along said transverse dimension, said thirdregion encompassing said second surface and having a lower fillercontent than said second region, and wherein a minimum filler density isat said second surface.
 8. The composite article of claim 7 wherein saidsecond region is substantially larger than said first and third regions.9. The composite article of claim 7 wherein said density gradient islocated in said first and third regions.
 10. The composite article ofclaim 7 wherein said first and third regions include an additive.
 11. Anon-laminated composite article having first and second opposingsurfaces defining a transverse dimension, said non-laminated compositearticle comprising a matrix and a filler material embedded in saidmatrix and defining first and second regions juxtaposed along saidtransverse dimension wherein said first region encompasses said firstsurface, and wherein said first region has a filler-to-matrix ratio thatvaries along said transverse dimension, said filler-to-matrix ratiobeing at a minimum at said first surface.
 12. The non-laminatedcomposite article of claim 11 wherein said transverse dimension is thethickness of said non-laminated composite article.
 13. The non-laminatedcomposite article of claim 11 wherein said first region has a lowerfiller content than said second region.
 14. The non-laminated compositearticle of claim 11 wherein said second region is substantially largerthan said first region and encompasses said second surface.
 15. Thenon-laminated composite article of claim 11 wherein said first regionincludes an additive.
 17. The non-laminated composite article of claim11 wherein said non-laminated composite article further defines a thirdregion juxtaposed with said second region along said transversedimension, said third region encompassing said second surface, andwherein said third region has a filler-to-matrix ratio that varies alongsaid transverse dimension, said filler-to-matrix ratio of said thirdregion being at a minimum at said second surface.
 17. The non-laminatedcomposite article of claim 16 wherein said first and third regions havea lower filler content than said second region.
 18. The non-laminatedcomposite article of claim 16 wherein said second region issubstantially larger than said first and third regions.
 19. Thenon-laminated composite article of claim 16 wherein said first and thirdregions include an additive. 20-22. (canceled)